Telephone system



T. F. QRQQKER TELEPHONE SYSTEM Filed Oct Ap'm l 13, 1932 3 Sheets-Sheet Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Thomas F. Crocker, Chicago, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application October 13, 1932, Serial No. 637,578

l 12 Claims. (Cl. 179-27) This invention relates to telephone systems in general and is concerned particularly with improvements in the circuits and apparatus employed in automatic telephone systems for extending connections from the toll switchboard to subscribers lines..

The object of' the invention is to simplify and improve the equipment required for toll service by making it less expensive to install and maintain and more eiiicient and reliable in operation. This object is accomplished in part by arranging the circuits so that talking current for called subscribers is supplied from the toll service trunk instead of from the transmission selectors or cord circuits as has been the practice heretofore. The toll switch train, accordingly, requires only simple and inexpensive selectors and the usual toll connectors. This arrangement constitutes one of the main features of the invention.

Another feature of the invention is the arrangement whereby the switching overv of the toll service apparatus from operating position to talking position is controlled in a very simple and reliable manner over the same conductor used for controlling the ringing.

The features of the invention together with the operation of the circuits and apparatus emv bodymg the same, will be described hereinafter,

reference being had to the accompanying draw- 39 ings, comprising Figs. 1 to 3, inclusive. The drawings should be arranged in numerical order with Fig. 1 at the left, Fig. 2 in the center, and Fig. 3 at the right.

Referring now to Fig. 1 there is shown the relay equipment T for a toll service trunk which terminatesl at a toll switchboard in jack J and at an automatic exchange inthe toll selector S shown in Fig. 2. A cord circuit C, of which only a part has been shown, may be of any suitable type, such, for example, as the cord circuit disclosed in applicants Patent No. 1,771,842, granted July 29, 1930.

Fig. 2 shows a toll selector S which terminates the toll service trunk shown in Fig. 1. This switch is similar to the ordinary Strowger type selector switch commonly used for local service with the addition of a. fourth wiper and an extra set of contacts on the switching relay for extending the control conductor. Selector S is shown as having access to toll connectors including the one shown in Fig. 3. When used in a larger system than the one chosen to illustrate the invention, one or more similar selectors will be interposed between selector S and the connectors.

Fig. 3 shows a ten-party toll connector C and an ordinary suscribers line and substation A. This connector is similar to that disclosed in Patent No. 1,811,444, granted June 23, 1931, to V. S. Tharp, modified for ten-party service and to adapt the switch for operation with the toll service trunk comprising a part ofthe present invention.

The operations involved in establishing a toll connection over the circuits and apparatus comprising the invention, will now be described in detail. By way of illustration it will be assumed that a toll operator has answered an incoming toll call for the subscriber at station A with the cord circuit C. The operator will insert the calling plug P of the cord circuit into the jack of an idle toll service trunk, for example, jack J of trunk T. The insertion of the plug into the jack closes the jack spring contacts 14 thereby completing a circuit for relay 1 which operates. Re- 75 lay 1 applies ground to holding conductor 23 at contacts 25, prepares a holding circuit for itself at contacts 6, applies ground to the lower Winding of sleeve relay 2 at contacts 7, and prepares a holding circuit for relay 4 at contacts 26. Sleeve 80 relay 2 now operates, due to its lower winding being energized from battery on the sleeve of the cord circuit. The lower winding of relay 2 has relatively high resistance so that a current flow in the sleeve circuit is not sumcient to permit S5 supervisory lamp L to light at this time. Relay 2, on operating, disconnects the trunk conductors 2l and 24 from the tip and ring springs of the jack at contacts 19 and 18 and at contacts 20 and 17 lconnects the repeating coil between the incoming and outgoing ends of the trunk. Line relay 202 of selector S (Fig. 2) now operates over a circuit which may be traced from battery, upper winding of the relay, contacts 226, conductor 21, contacts 31, upper right hand winding of the repeating coil, contacts 8, resistance 15, contacts 11, lower right hand winding of the repeating coil, contacts 17 and 34, trunk conductor 24, contacts 229, lower winding of relay 202, to ground. Relay 202 completes an obvious circuit to relay 203 at contacts 230. Relay 203 operates, applies ground to the holding conductor at contacts 232, and prepares the impulsing circuit atcontacts 233.

The foregoing operations take place in response to the connection of the cord circuit with the trunk. The operator now dials the first digit of the called number. When the dial is turned oi normal the talking strands at the cord, in well known manner, are looped through the impulse contacts of the dial and battery is disconnected from the sleeve circuit. Relay 2 of the cord circuit accordingly restores and extends the trunk conductors to the ring and tip springs of the jack, and thence over the ring and tip contacts of the plug and the talking strands of the cord to the impulse contacts of the dial. The dial on returning to normal interrupts the circuit over which relay 202 of the selector is held operated and the relay responds in the usual manner. Each time relay 202 releases a circuit is completed by way of contacts 209, 231,233, windingY of series relay 204, winding of vertical magnet VM, to battery. The vertical magnet raises the wipers of the switch step by step to the level indicated by the digit dialed. Relay 204 energizes in series with the vertical magnet and, due to its slow-releasing characteristics, remains operated throughout the series of impulses. Upon the wipers leaving normal position, vertical olf-normal contacts 213 close and complete a circuit by way of contacts 212 and 232 for relay 205.v Relay 205 operates and by closing contacts 236 prepares a holding circuit for itself independent of contacts 212. A circuit for the rotary magnet is prepared at contacts 235. Shortly after the last impulse of the series, relay 204 releases and by closing contacts 211 completes the circuit for the rotary magnet. The rotary magnet energizes, steps the wipers of the switch in on the i'irst set of contacts in the level to which the wipers are raised by the first digit, and opens the circuit of relay 205. The further operations now depend upon the busy or idle condition of the trunk terminating in the rst set of contacts. Assuming` that the trunk is busy, wiper 220 will find ground on the test contact which, by way of contacts 207, interrupter contacts of the rotary magnet, and vertical off normal contacts 213 re-operates relay 205. Relay 205 again closes the circuit of the rotary magnet which advances the wipers another step to the succeeding contact set. The foregoing operations are repeated until the wipers nd an idle trunk or until the wipers are rotated past the last trunk in the group.

When no idle trunk in the level called is available, the wipers of the switch are rotated past the last trunk in the group and overflow contacts 214,-216 are closed. The closure of the contacts 216 connects interrupter INT to controlconductor 22 which extends by way of contacts 13 and the upper winding of relay 4 of trunk circuit to ground. The rst connection of battery to this circuit by the interrupter energizes relay 4 which locks over its lower winding by way of contacts 12 and 26. Relay 4 at contacts 29 shunts the lower high resistance winding of relay 2 with the upper low resistance winding of the relay. This, however, is without eiect until the operatorA restores the cord circuit to talking conditionA and recloses the sleeve circuit. When the wipers leave the last grounded contact of the level, relay 201 will operate in series with relay 205. yRelay 205, however, does not operate due to the high resistance of relay 201. The interrupted current from interrupter INT produces a busy tone which is applied by way of condenser 217, contacts 227, conductor 21, thence over the loop through the cord circuit, conductor 24; overow contacts 214, and a resistance to ground. This tone noties the operator of the busy condition of the trunk group. Upon receiving the busy signal, the operator is expected to release the connection as will be described subsequently.

Returning now to the point at which selector S started its trunk hunting operation, it will be assumed that the trunk comprising conductors 222-225 is idle. Wiper 220 will find no ground on the test contact of this trunk and relay 201 will operate in series with relay 205 as above described. Relay 201 connects trunk conductor 2l and 24 through to the upper and lower wipers of the selector via contacts 227 and 228, disconnects relay 202 from the incoming trunk at contacts 226 and 229, extends control conductor 22 to wiper 219 by way of contacts 206, and disconnects test Wiper 220 from its own lower terminal at contacts 207 and at contacts 208 connects the Wiper to holding conductor 23. Relays 202 and 203 restore but the selector remains in operated position as the release circuit is now open at contacts 209.

Referring now to the connector, the extension of the trunk conductors by way of wipers 218 and 221, conductors 222 and 225, contacts 336 and 339, upper and lower windings of relay 302 to battery and ground, energizes the relay. Relay 302 completes the circuit of relay 303 at contact 340. The relay 303 operates, applies ground to the local holding circuit at contacts 343 and by way of vertical off normal contacts 351, completes a circuit for relay 305. Ground is applied to control-conductor 223 at contacts 312 to shunt relay 4 of the trunk circuit, which, as before explained, is connected to the control-conductor of the trunk. Relay 303 also completes a circuit for relay 304 at contacts 314 and prepares the impulsing circuit at contacts 344. Relay 305 operates, prepares a holding circuit for itself at contacts 319 and connects vertical magnet VM to the impulsing circuit at contacts 364.

The operator now dials the second digit of the called number, interrupting the circuit of relay 302 which repeats the impulses to the vertical magnet over a circuit extending via contacts 311, 341, 344, 369, 321, 334 and 364,-to the magnet. The magnet raises the wipers of the switch to the level indicated by the number dialled. Slow releasing relay 308 energizes in parallel with the magnet and remains energized throughout the series of impulses. Relay 305 remains operated during this series of impulses over its holding circuit including contacts 319 `and 326. The original' energizing circuit of relay 305 is opened at oilnormal contacts 351 which open when the wipers leave normal position. Relay 308 releases shortly after the last impulse of the series and opens the circuit of relay 305 which also releases. Rlay 305 connects rotary magnet RM to the impulsing circuit at contacts 365.

The third series of impulses are repeated by relay 302 to rotary magnet RM, which steps the wipers of the switch to the contacts in which the called line terminates. Relay 308 again operates, connects busy test relay 307 to test wiper 358 at contacts 324, and short circuits contacts 321 by closing contacts 327 to prevent a momentary interruption of the impulsing circuit in case relay 307 operates as the test wiper passes over busy contacts. In case the called line is busy when the connection is extended in the manner described, relay 307 energizes from the ground encountered on the test contact by wiper 358. Relay 307 locks up by way of contacts 373 and 323 upon the release of relay 308 which occurs shortly after the last impulse of the series, connects interrupter INT to the upper talking conductor of the switch at contacts 371, and opens the impulsing circuit at contacts 321. A circuit is also completed for relay 301 by way of contacts 313,

320 and 325. Relay 301 operates and locks to holding conductor 224 at contacts 310. Incoming trunk conductors 222 and 225 are disconnected from line relay 302 at contacts 336 and 339 and at contacts 337 and 338 are connected through to the talking conductors of the connector. Relay 302 releases and opens the circuit of relay 303. Relay 303 releases and among other things, removes ground from the control-conductor 223 by opening. contacts 312 and 314. Since relay 304 is operated its upper winding is connected to control-conductor 223 by way of contacts 318 and relay 4 of the trunk circuit will now operate in series with the upper winding of relay 304. Relay 4 changes over the trunk from operating and talking position as previously described so that when the operator restores her dialling key to normal the low resistance circuit to the upper winding of relay 2 will permit the supervisory lamp L to light and give her the usual supervision. In this case, however, the interrupter INT has been connected by way of contacts 371 and 337, trunk conductor 222, wiper 218, and contacts 227 of selector S, trunk conductor 21, contacts 31, upper right-hand winding of the repeating coil of trunk T, contacts 9, upper winding of relay 3 to ground. Relay 3 accordingly operates intermittently to open the low resistance circuit to thev upper winding of sleeve relay 2, thereby causing lamp L to flash. This flashing signal indicates to the operator that the called subscribers line is engaged. The operator will then release the connection by withdrawing the plug of the calling cord lfrom the jack.

In case the called line is idle when the connection is extended thereto as above described, testr wiper 358 will find no ground on the test contacts and relay 307 accordingly is not operated. When relay 308 restores shortly after the last` impulse of the series, a circuit is completed for the upper winding of relay 309 from grounded holding conductor 224, contact 372, upper winding of the relay, contacts 322 and 329, test wiper 358 and thence to battery through the cut-olf relay of the called line. Relay 309 operates, completes a locking circuit for its lower. winding at contacts 332, closes the talking conductors of the switch through to wipers 357 and 359 at contacts 328 and 335, applies ground directly to the test wiper at contacts 330 to fully operate cut-0E relay of the called line, and transfers the impulsing circuit from the rotary magnet to the auxiliary switch stepping magnet ASM at contacts 333.

The operator now Vdials the last digit of the called number, and the impulses are repeated by relay 302 to magnet ASM. Wipers 355 and 356 of the auxiliary switch are stepped in accordance With the dialled digit and auxiliary switch oli-normal contacts AON close when the wipers leave normal position. If the last digit is any of the digits 1 to 5, wiper 356 will connect with a ringing current generator G1-G5, and Wiper 355 will have no function to perform. Shortly after the last impulse of the series, relay 308 restores and completes a circuit byhway of contacts 325 and off-normal contacts 354 for relay 306. Relay 306 operates, prepares the ringing circuit by closing contacts 367 and completes a circuit at contacts 368 for relay 301. Relay 301 operates, locks to grounded holding conductor 224 at contacts 310, disconnects relay 302 fromvthe trunk at contacts 336 and 339. Relays 302 and 303 restore but the switch does not release at this time due to contacts 311 being open. Relay 303 re- -moves ground from control-conductor 223 at contacts 312, opens the original'energizing circuit of relay 304 at contacts 314, opens the local holding circuit at contact 343 and prepares the release circuit at contacts 345. The control-conductor 223 extends back through the selector to ground through the upper winding of relay 4 of the trunk circuit. The removal of ground from this conductor and from the original energizing circuit of relay 304 permits relay 4 to operate in series with the upper winding of relay 304.V Relay 304 therefore remains operated after relays 302 and 303 release and maintains the ringing circuit open to prevent the called subscriber from being signalled at this time. Relay 4 closes the supervisory circuit at contacts 29 and connects battery feed relay 3 to the talking conductors of the trunk. The operator, on restoring her cord circuit to talking position, now receives line seizure supervision consisting of the steady lighting of lamp L. l'

When the operator is ready to signal the called subscriber, she operates her ringing key in the usual manner, which increases the resistance in the sleeve circuit thereby causing sleeve relay 2 to restore and complete a circuit for relay 5 by way of contacts 30 and 16, ring contacts of the jackv and plug to battery at the ringing key of the cord circuit. Relay 5 now operates, applies ringing current to the two trunk conductors although this is without utility in the present instance, and opens the control circuit at contacts 1.3. The opening of the control circuit permits ring-cut-oi relay 304 of the connector to release. Relay 304 on releasing completes the ringing circuit and ringing current is now applied to the called line over one of two circuits depending upon the value of the last or ringing curent selecting digit of the called number. For digits of lower value than the digit 6 the ringing circuit may be traced from the selected ringing current lead Gl-G5, wiper 356, contacts 367, 348, 315 and 328, wiper 357, line conductor 362, through the bell and condenser at the called station, conductor 360, wiper 359, contacts 335, 347 and 353, lower Winding of relay 304\, to battery. In case the lastl digit is one of the digits 6 0, relay 305 will be operated due to wiper 355 stopping on a grounded contact. In this case the ringing circuit will extend from the selected generator lead G1-G5, contacts 367, 349, 347 and 335', wiper 359, line conductor 360, through the bell and condenser at the called station, conductor 362, wiper 357, contacts 328, 315 and 352, lower Winding of relay 304 to battery. The required party on the line is signalled in the manner described and when the call is answered, relay 304 operates over the direct current circuit through the called station. Relay 304 again locks to conductor 223, opens 'the ringing circuit at 'contacts 315 and 347, disconnects ring-back tone from the trunk at contacts 317, and extends the talking conductors to the wipers via contacts 316 and 346.

It will be recalled that battery feed relay of the trunk circuit was connected across the talking conductors of the trunk upon the operation of relay 4. This relay now operates over the called subscribers loop and opens the low resistance -sleeve circuit to extinguish the supervisory lamp L. This indicates to the operator that the coil has been answered after which she will free her set from the cord circuit and the connection will then proceed in the usual manner.

At the termination of the call, the called subscriberrestores his receiver and relay 3 releases.

CFI

The low resistance sleeve circuit is again closed and lamp L lights to give the operator disconnect supervision. The connection may then be released by withdrawing the plug of the cord from the jack. Relay 1 restores and removes ground from holding conductor 23 at contacts 25, opens the sleeve relay circuit at contacts 'l and opens the holding circuit of relay 4 at contacts 26. These relays restore and the trunk is in normal condition. In the selector, relay 201 releases when ground is removed from holding conductor 23 and'completes the release magnet circuit by way of contacts. 209, 231 and 234 and olf-normal contacts 210. Release magnet RLM restores the switch to normal position in the' usual manner. In the connector relay 301 releases when ground is removed from conductor 224 and completes the release magnet circuit by way of contacts 311, 341, and 345, and olf-normal contacts 342. The release magnet RLM restores the switch wipers to normal position in the usual manner. The auxiliary switch release magnet ARM is energized in parallel with the magnet RLM by. way of contacts 370 and restores the auxiliary switch wipers to normal in the usual manner. The opening of contacts 354, upon the auxiliary switch wipers reaching normal position, permits relay 306 to restore and open the release magnet circuit at contacts 370. Relay 309 which has been held operated in parallel with relay 301 releases upon the removal of ground from holding conductor 224. Relay 305 in case it has been operated, releases when wiper 355 is restored from the grounded contacts. Relay 304 releases due to the opening'of the control circuit at the selector by the release of relay 201.

In case the operator should withdraw the plug of the cord circuit from the jack at any time prior to the called subscribers restoringhis receiver, the connection is not released due to the holding circuit for relay l which. is completed over contacts 29, 28 and 6.' Relay 1 will maintain the ground on the holding conductor 23 and the switches will remain operated under control of the called subscriber. When the called subscriber eventually restores his receiver battery feed relay 3 releases, and the release of the connection takes place in the manner described.

What is claimed is:

1. In a telephone system, a toll trunk line. an automatic switch terminating the trunk line, a cord circuit adapted to connect with the trunk line, means including the cord circuit, the trunk line, and the switch for extending a connection to a calledline, and means interspersed between the cord circuit and the switch for supplying di.- rect current to the called line.

2. In a telephone system, va tool switchboard, a cord circuit, a trunk extending from the switchboard to an automatic switch, a second automatic switch, means for extending a connection via said cord circuit, said trunk, and said switches to a called line, a battery feed bridge, and means controlled from said second switch for connecting said bridge to said trunk between said cord circuit and said first switch.

,3. In a telephone system, a trunk, a switch, means for extending a connection over the trunk to the switch, means controlled over the trunk for setting the switch to further extend the connection, a supervisory relay associated with the trunkv and connected to one trunk conductor, a

r-ing-cut-off relay in the switch connected to said one trunk conductor, and means in the switch for shunting said supervisory relay and for energizing said ring-cut-oi relay during the setting of the switch.

4. In a telephone system, a, trunk, a switch,

means for extending a connection over the trunk to the switch, means controlled over the trunk for setting the switch to further extend the connection, -a relay associated with the trunk and connected to one trunk conductor, a second relay in the switch connected to said one trunk conductor, means for shunting said first relay and for energizing said second relay during the setting of the switch, and means responsive to the completion of the setting of the switch for removing the shunt from said rst relay to permit the two relays to energize in series.

5. In a telephone system, a switchboard, a signal at the switchboard, a trunk including a control conductor terminating at the switchboard, a switch, means for extending a connection over said trunk and said switch, means in the switch for controlling said signal over said conductor, and means in said switch controlled from the switchboard over said conductor for signalling the called line.

6. In a telephone system, a switchboard, a signal at the switchboard, a supervisory relay for controlling said signal, a trunk including a control conductor terminating at the switchboard, a switch, a ring-cut-off relay in said switch, means for extending a connection over the trunk and said switch to a called line, means responsive to the completion of the connection for energizing said two relays in series over said control con'ductor, and means for opening said control conductor to release said ring-cut-oi relay and signal the called line.

7. In a telephone system, a toll trunk, a toll switch train adapted to be controlled over the trunk, a supervisory relay in the trunk, means in the last switch of the train for shunting said relay to prevent its operation during the setting of the switch, and means responsive to the completion of the setting of said switch for removing the shunt from said relay to energize the same.

8. A telephone system as claimed in claim 7 in which the supervisory relay upon energizing connects a battery feed bridge to the trunk.

9. A telephone system as claimed in claim 7 in which the supervisory relay upon energizing locks up over a circuit independent of its original energizing circuit.

10. A telephone system as claimed in claim '7 in which the supervisory relay upon energizing completes a circuit for operating a signal.

11. In a telephone system, a toll trunk, a toll switch train adapted to be controlled over the trunk, a supervisory relay in the trunk, a ringcut-off relay in the last switch of the train, means in the last switch of the train for shunting said first relay to prevent its voperation during the setting of the switch, and means responsive to the completion of the setting of said last switch for removing the shunt from said rst relay and for energizing both said relays in series.

12. A telephone system as claimed in claim 11 in which the series connection between the two relays is opened to release the ring-cut-olf relay and initiate the signalling of a called party.

THOMAS F. CROCKER.

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